Danazol (200 mg/day) or placebo was administered to patients with premenstrual syndrome from the onset of symptoms until the onset of menses, for two cycles each, in a prospective, double-blind, crossover design. Eleven of 14 patients improved on danazol. The symptom scores with danazol were significantly lower than those with placebo (P < .035). No side effects were reported from the medication. We conclude that danazol, given periodically and in a relatively low dose, appears to have a beneficial effect in the treatment of premenstrual syndrome.